In a conventional combustion engine, energy from fuel is converted to useful work by a subsonic combustion process, referred to as deflagration. In contrast, a PDE operates by means of a supersonic combustion process, referred to as detonation (or quasi-detonation). The detonation may be initiated, for example, by igniting a fuel and air (or oxidizer) mixture in a detonation chamber. For practical purposes, such detonations must be repeated at a high frequency.
Compared to conventional combustion engines, PDEs have higher thermodynamic efficiencies and fewer moving parts, among other advantages. Nonetheless, various challenges remain in achieving a PDE of sufficient practical applicability. Areas for improvement include achieving detonation, using liquid fuels, and increasing operating frequency (or, in other words, decreasing the cycle time), among others.